The relaxation processes of orientation and disorientation of melts of high-density polyethylene (HDPE) and polyamide-6 (PA6) blends compatibilized with a compatibilizer precursor (CP) of HDPE-grafted maleic anhydride (HDPE-g-MAH) were investigated in a restricted channel using real-time ultrasonic technique. The experimental results showed that the evolution of ultrasonic velocity of HDPE/PA6 blends during the orientation or disorientation processes could be described by the exponential equation from which the maximum orientation degree and relaxation time could be obtained. Subsequently, the effects of CP on the relaxation processes of orientation and disorientation were Studied. In addition, the relations of the CP content and the morphology and viscosity were investigated by scanning electron microscope analysis and rheological tests. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 320-327, 2010